I'm currently running Mac OS 10.5.8 on my 2008 vintage iMac. With 2.4 GHz Intel Core 2 Duo processor and 4 GB 800 MHz DDR2 SDRAM, what's the best OS I can run. Been having a few issues, like I can't use the latest version of Flash, which I need. Is an upgrade to 10.6.3 worth $106 I can get it for at Amazon? Other advice?